This section provides background information related to the present disclosure which is not necessarily prior art.
Underground utility lines are sometimes installed using any of a variety of trenchless installation technologies, including horizontal boring technologies. Horizontal boring technologies provide efficient and cost effective ways to install gas, water, electric and communications lines, particularly when it is difficult or cost prohibitive to plow or trench the ground, such as when there are ground obstructions (e.g., a road, sidewalk, driveway, or landscaping) along the path of the utility line that prevent those techniques. Some horizontal boring technologies include underground pneumatic boring, auger boring, wet boring, horizontal directional drilling (HDD), impact moling, pipe jacking and microtunneling.
The process of underground pneumatic boring involves launching a pneumatic boring or piercing tool that creates a horizontal bore hole along a straight path to create a tunnel through the ground. A utility line (e.g., for gas, water, electric or communications) can then be pulled back through the tunnel for installation underground. For example, existing utility lines and surface obstacles to be traversed by the utility line are surveyed and a path for the new utility line is chosen. Two pits are excavated on opposite sides of the obstacle, including one pit at an origin of the path (the entrance pit) and one pit at a target destination of the path (the exit pit). The pits are large enough to fit the boring tool and to permit an operator to work. The pits are also deep enough so that as the boring tool creates the tunnel, the surface of the ground above the tunnel remains undisturbed.
The boring tool comprises a pneumatically-operated boring tool that cuts through soil, rock, etc. The boring tool is connected to a supply of compressed air by a hose. A guide tool and a sighting device are used to align the boring tool along the desired path and toward the intended destination. The boring tool is then activated to cut an underground bore, advancing through the wall of the entrance pit with the air supply hose following behind the boring tool. Once the boring tool has progressed beyond the guide tool, the location of the boring tool is tracked through the ground with a radio frequency receiver that detects a radio signal generated by a radio transmitter built into the boring tool.
When the boring tool reaches the target destination, a tunnel is created between the entrance pit and the exit pit and beneath the surface obstacle. The boring tool is removed from the air supply hose and the utility line is attached to the air supply hose (e.g., by taping the utility line to the hose). The hose and the utility line are pulled back through the tunnel together, thereby installing the utility line underground.
Underground pneumatic boring, however, has drawbacks which can result in difficulties in completing a bore for an underground utility line. For example, the boring tool is not steerable, and once the boring tool has exited the guide tool the operator no longer has control over the trajectory of the boring tool. Consequently, the boring tool can be deflected from the desired path by rocks and different soil densities, for example. Even minor deflections can cause significant deviations from the desired path over long distances. Consequently, the boring tool could unintentionally cross the path of other already existing underground utilities. Therefore, and notwithstanding the fact that existing underground utility lines are located and marked from above ground before the pneumatic boring underground is carried out, it is possible that the boring tool can tunnel through an existing utility line, such as a sanitary sewer line. Consequently, the newly installed utility line may be run through the existing sewer line. In such an instance, a crossbore—that is, an intersection of two or more underground utilities—is created.
A significant concern for the underground utility construction industry, regardless of the horizontal boring process employed, is unknowingly tunneling through a sewer line and thereafter running a utility line, such as a natural gas pipeline or power line, through the sewer line. The crossbored utility line may remain in place for months or years before a blockage develops in the sewer line. Then, in the process of clearing the sewer line, the utility line can be severed, ruptured, or otherwise damaged by a power drain auger or other tool or machine that is used to clear the sewer line.